Heat pumps and fluid pumps therefor

ABSTRACT

A fluid pump for pumping a fluid. One or more piston-cylinder arrangements each include a respective cylinder portion, a respective head portion and a respective piston portion together defining a respective pumping chamber. One or more connecting arrangements connect a crank member to the one or more piston-cylinder arrangements to drive the respective piston portion of each of the one or more piston-cylinder arrangements. A housing and the respective piston portion of each of the one or more piston-cylinder arrangements together house the crank member in an interior. The interior is sealed to capture blow-by. A transmission is arranged to transmit power, for rotating the crank member, into the housing magnetically, electrically or both.

FIELD OF THE INVENTION

Various aspects of the invention relate to heat pumps and fluid pumpsand various components and methods therefor. Some aspects of theinvention are applicable beyond the context of such pumps.

BACKGROUND TO THE INVENTION

FIG. 1 illustrates a heat pump 1 including a fluid circuit 3. The pump 1may be employed as an air conditioner to cool a truck cabin and isdescribed herein in that context by way of example only.

Spaced about the fluid circuit 3 are a compressor 5, a heat exchanger inthe form of condenser 7, an expansion valve 9 and a heat exchanger inthe form of evaporator 11. The compressor receives and increases thepressure and temperature of refrigerant vapor. The refrigerant is thencooled through the condenser. An exterior fan 7 a is employed to driveair through the condenser to accept heat.

The compressor 5 is a form of fluid pump. For the avoidance of doubt‘fluid’ and similar terminology is used herein in its broadest sense torefer to flowable substances such as liquids and gases, and mixturesthereof.

Liquid high-pressure refrigerant emerges from the condenser. As such theportion of the fluid circuit 3 from the compressor 5 to the expansionvalve 9 is known as the high-pressure side of the circuit. The otherside of the circuit, from the expansion valve 9 to compressor 5, isknown as the low-pressure side of the circuit.

The expansion valve reduces the pressure of the refrigerant. Thelow-pressure refrigerant emerging from the expansion valve is typicallya mixture of liquid and vapor.

Through the evaporator 11 the refrigerant is heated. An interior fan 11a drives air through the evaporator 11 to reject heat to therefrigerant. The air conditioner may be either a recirculating system,wherein the fan 11 a recirculates air within the cabin, or a fresh airsystem wherein the fan 11 a draws air from outside the cabin and drivesthe air into the cabin of the vehicle. Refrigerant vapor is conveyedfrom the evaporator to the compressor to complete the circuit 3.

FIG. 16 illustrates an existing evaporator 211 including an inlet 213and an outlet 215 and copper tubing 217 defining a flow path portion 217from the inlet to the outlet. The fluid path portion consists of aseries of vertical runs 219 connected by bends 221.

The tubing is supported by support structure 223 and carries a set ofhorizontal, approximately planar aluminium fins. Typically a fan isarranged to convey air through the evaporator 11 in a direction normalto the page.

Air conditioners are often thermostatically controlled whereby they areperiodically activated and deactivated based on a measured temperaturerelative to a desired temperature.

FIGS. 2 and 3 illustrate selected components of the inventor's owncompressor 5. The compressor 5 includes a housing 13 also known as a‘block’ or ‘crank case’. A main body 15 of the housing 13 is machinedfrom aluminium billet.

A respective piston-cylinder arrangement 17 sits at each end of thehousing 13. Each piston-cylinder arrangement 17 incorporates a sleeve 19pressed into the body 15 and defining a cylinder 21. The arrangement 17further includes a piston 23 and a head portion 25. The piston 23 ismounted to slide within the cylinder 21. The cylinder 21, piston 23 andhead portion 25 together define a pumping chamber 27.

The sleeves 19 also form parts of the housing.

A crank member 29 is mounted within the housing 13. The crank memberincludes an input shaft 31 mounted to rotate within bearings 33. Thecrank member 29 further includes a crank pin 35 eccentric to the inputshaft 31. The housing 13 further includes a tubular drive-adaptor 37embracing the input shaft 31 and sealingly engaging the body 15. A seal39 is mounted within the adaptor 37 and sealingly engages the inputshaft 37. The housing 13 and pistons 23 together house the crank member29 in an interior 41 that is sealed to capture blow-by.

For the avoidance of doubt, ‘blow-by’ is used herein in its ordinarysense in this art to refer to the leakage of fluid from a pumpingchamber and past a piston.

The adaptor 37 includes a mounting flange co-operable with an electricmotor. The input shaft 31 is fitted with a coupling 43 to connect theinput shaft 31 to the output shaft of the electric motor. The electricmotor is a 12V DC motor sold by Allied Motion™ under the part no.PJ2P021Q.

A connection arrangement 45 connects the crank shaft 29 to the pistons23. The connection arrangement 45 includes a pair of conrods (i.e.connecting rods). One end of each of the conrods is journaled to thecrank pin 35 with suitable roller bearings. The other end of each of theconrods is connected to a respective one of the pistons 23 via arespective gudgeon pin.

Head portion 25 incorporates a main body 25 a machined from aluminiumbillet and a stainless steel valve plate 25 b (see FIG. 6 ) sandwichedbetween the main body 25 a of the head portion 25 and the main body 15of the housing 13.

A pair of simple holes 25 c, 25 d open through the plate 25 b inregister with the pumping chamber 27. A respective simple hole 25 epasses through each corner of the plate 25 b and a pair of holes 25 f,25 g open through the plate towards the rear of the compressor 5.

The holes 25 e accommodate head bolts 25 h (FIG. 2 ) engageable withthreaded bores of the body 15 to retain the head 25.

A petal 46 (FIG. 8 ) co-operates with the port 25 d to form a reed valvedefining an inlet into the pumping chamber 27. The petal 46 is formed of0.15 mm thick SANDVIK HIFLEX FLAPPER VALVE STEEL™. The petal includes aroot portion 46 a having side extensions 46 b and dimensioned to sitwithin a complementary recess formed within an end face of the cylindersleeve 19. The plate 25 b overlies the root portion 46 a to hold thepetal in place. The petal projects from its root portion 46 b across thecylinder 21 a to position port occluding portion 46 c of the petal inregister with the port 25 d. The occluding portion 46 c seals againstthe surface of the plate 25 b to prevent fluid escaping the pistonchamber 25 via the port 25 d. When the piston 23 is moving away from thehead portion 25 (to increase the volume of the pumping chamber 27) thepetal 46, or more specifically its occluding portion 46 c, is liftedaway from the plate to allow fluid into the pumping chamber 27 via theport 25 d.

The petal 46 has an opening 46 d positioned to sit in register with theopening 25 c so as not to occlude the opening 25 c.

A petal (now shown) similar to the petal 46 is clamped between the mainbody 25 a and the plate 25 b to co-operate with the port 25 c to definean outlet from the chamber 27. The petal of the outlet is positioned soas not to overlie the port 25 d such that there is no need for anopening akin to the opening 46 d.

The main body 25 a has a contoured interior surface shaped to sealinglyengage the plate 25 b to define a flow path from the outlet 25 c to thehole 25 f and another flow path from the hole 25 g to the inlet 25 d,46. The holes 25 f, 25 g sit in register with galleries running the fulllength of the body 15. At the other end of the body 15 is a head portion25′ similar to the head portion 25 and including apertures akin to theapertures 25 f, 25 g opening to the same galleries. The lower gallery(in register with the 25 g) is tapped at the rear of the body 15 todefine an inlet of the compressor 5. The gallery in register with thehole 25 f is tapped at a rear of the body 15 to define an outlet of thecompressor 5.

Reverse cycle air conditioners are heat pumps that can pump heat ineither direction. The heat pump of FIG. 1 could be made reversible byadding a reversing valve and replumbing the compressor 5. FIGS. 4 and 5illustrate an existing reversing valve 47 in two distinct operatingmodes. The valve 47 incorporates a tubular housing 49 and flow ports 5_(out), 5 _(in), 7′, 11′ opening to an interior of the housing. Thehousing 49 houses a shuttle 51.

In the first mode of FIG. 4 the shuttle 51 is positioned to:

-   -   mutually connect the ports 5 _(out), 7′ whereby a first        first-mode flow path FP_(FM1) for connecting the outlet of the        compressor to the condenser 7 is defined; and    -   mutually connect the ports 5 _(in), 11′ whereby a second        first-mode flow path FP_(FM2) for connecting the evaporator to        the inlet of the compressor is defined.

The shuttle 51 resides within the tubular housing 49 and has arespective piston 51 a, 51 b at each of its ends defining end chambers51 c, 51 d. The end chambers 51 c, 51 d are alternately connected to thehigh-pressure half of the fluid circuit 3 via a small three-way solenoidvalve (now shown) and capillary lines. In the first operating mode, thechamber 51 d is connected to the high-pressure refrigerant whilst thechamber 51 c is isolated therefrom whereby the refrigerant drives theshuttle 51 towards the left as illustrated in FIG. 4 .

To change modes, i.e. to reverse the direction in which the pump 1 pumpsheat, the position of the three-way solenoid valve (now shown) isreversed to switch the high-pressure refrigerant from the chamber 51 dto the chamber 51 c whereby the refrigerant drives the shuttle 51towards the right (as drawn) to the position of FIG. 5 wherein theshuttle 51 occludes the first-mode flow paths FP_(FM1), FP_(FM2) andopen are second-mode flow paths FP_(SM1), FP_(SM2) for connecting theoutlet of compressor to the heat exchanger 11 (which becomes acondenser) and connecting the inlet of the compressor to the heatexchanger 7 (which becomes an evaporator).

To the inventor's knowledge, all commercially available reverse cycleheat pumps incorporate this style of reversing valve. Such valves arewidely regarded as simple and effective and also cost-effective in thatthe only electromechanically-driven valve element is the valve elementof the small solenoid valve. The larger valve element, the shuttle 51,is driven by the refrigerant. In effect, the shuttle 51 is moved by thecompressor 5 which makes efficient use of the available resources.

The inventor's compressor 5 is significantly more efficient thancomparable compressors that dominate the market. To the inventor'sknowledge, the most popular comparable compressor (at least in theAustralian market) is sold by Danfoss™ under the part number BD350GH.When the inventor tested that compressor in a heat pump, the heat pumppumped 979 watts of heat and drew 32.5 amps of current corresponding toa power draw of 391 watts and a coefficient of performance of about 2.5.A compressor similar to the Danfoss™ BD350GH compressor sold under theBOYARD trade mark was also tested with similar results. When a variantof the compressor 5 having a bore of 16 mm and stroke of 8 mm wastested, the heat pump pumped 950 watts of heat and drew 14 ampscorresponding to a power draw of 185 watts and a coefficient ofperformance in excess of 5.

Nonetheless, the present inventor has recognised that furtherimprovements are possible. In particular, the present inventor hasrecognised scope a) for further efficiency gains, b) to reduce the riskof leakage, and c) to improve the reliability of the compressor.Likewise, whilst the reversing valves 47 are widely accepted in the art,the present inventor has recognised that in certain contexts they are asource of unreliability. Some of the inventor's advantageousdevelopments may be usefully applied in other contexts.

With the foregoing in mind the present invention in its various aspectsaims to provide improvements in and for valves, fluid pumps and/or heatpumps, or at least to provide alternatives for those concerned withvalves, fluid pumps and/or heat pumps.

SUMMARY

One aspect of the invention provides a fluid pump including one or morepiston-cylinder arrangements each including a respective piston portionand

a respective pumping chamber;a crank member;a housing; anda transmission;the housing together with the respective piston portion of each of theone or more piston-cylinder arrangements defining an interior in whichthe crank member is housed;the interior being sealed to capture blow-by; andthe transmission being arranged to transmit power, for rotating thecrank member, into the housing at least one of magnetically andelectrically.

The transmission may be a magnetic coupling including a rotatableportion outside the housing and a portion inside the housingmagnetically co-operable with, to be rotated by, the rotatable portion.The fluid pump may include an electric motor for driving the rotatableportion.

Alternatively the fluid pump may include an electric motor having insidethe housing each of a stator and a rotor. The transmission may includeat least one wire for the electric motor and entering the housing via asealed aperture.

Alternatively the transmission may include an electric motor having astator outside of the housing and a rotor inside the housing.

The fluid pump preferably includes two or more of the piston-cylinderarrangements. Optionally the crank member and one or more connectingarrangements, connecting the crank member to the respective pistonportions, are configured to move the respective piston portions of thetwo or more of the piston-cylinder arrangements in unison to holdsubstantially constant a volume of the interior. The one or moreconnecting arrangements may include a member having two ends and arespective one of the piston portions at each of the ends.

Preferably the fluid pump includes an electric drive motor. Preferablythe pump has a total weight, including the electric drive motor, notexceeding 10 kg. Most preferably the total weight does not exceed 6 kg

Another aspect of the invention provides a reed valve including

a port;a ridge surrounding the port; anda petal arranged to bear against the ridge to close the reed valve.

The ridge is preferably shaped to contact the petal along a line ofcontact not more than 0.5 mm thick.

Another aspect of the invention provides a fluid pump including

one or more pumping chambers;each of the pumping chambers having

-   -   a variable volume; and    -   a first reed valve defining one of an inlet to the respective        pumping chamber and an outlet from the respective pumping        chamber.

Preferably each respective one of the pumping chambers has a second reedvalve defining the other of the inlet to the respective pumping chamberand the outlet from the respective pumping chamber.

Another aspect of the invention provides a reverse cycle heat pumphaving a first mode of operation and a second mode of operation andincluding

a fluid circuit; anda pump-and-valve arrangement including

-   -   a fluid pump for pumping fluid about the fluid circuit; and    -   a reversing valve arrangement;        the reversing valve arrangement including    -   first-mode flow paths through which fluid flows when the pump is        in the first mode of operation; and    -   second-mode flow paths through which fluid flows when the pump        is in the second mode of operation;    -   one or more valve elements; and    -   one or more electromechanical drives;        the one or more electromechanical drives being arranged to        electromechanically drive the one or more valve elements    -   from one or more respective first-mode positions at which the        one or more valve elements occlude the second-mode flow paths;    -   to one or more respective second-mode positions at which the one        or more valve elements occlude the first-mode flow paths;        to reverse a direction of flow about the fluid circuit and        thereby switch from the first operating mode to the second        operating mode.

The reversing valve arrangement may include a pair of electromechanicalthree-way valves. Preferably the first-mode flow paths include

-   -   a first first-mode flow path for connecting an outlet of the        fluid pump to a first heat exchanger; and    -   a second first-mode flow path for connecting an inlet of the        fluid pump to the second heat exchanger;        the second-mode flow paths include    -   a first second-mode flow path for connecting the outlet to the        second heat exchanger; and    -   a second second-mode flow path for connecting the inlet to the        first heat exchanger; and        the reversing vehicle arrangement includes a respective        electromechanical valve for each of the first first-mode flow        path, the second first-mode flow path, the first second-mode        flow path and the second second-mode flow path is provided.

Preferably the fluid pump has a displacement of not more than 10 cc(0.61 ci), most preferably it is not more than 5 cc (0.31 ci).

Another aspect of the invention provides a heat pump including

a fluid circuit; anda fluid pump for pumping fluid about the fluid circuit;whereinthe heat pump is configured for evaporation of the fluid when the heatpump is in at least one operating mode of the heat pump;the fluid circuit includes a fluid circuit portion;the fluid circuit is configured for at least most of the evaporation tooccur along the fluid circuit portion; andthe fluid circuit portion is arranged for the fluid to flow upwardly, orat least horizontally, along substantially all of the fluid circuitportion when the heat pump is in the at least one operating mode of theheat pump.

The fluid circuit is preferably configured for at least 90% of theevaporation to occur along the fluid circuit portion. The fluid circuitportion may include a serpentine conduit along which the fluid flows.The serpentine conduit may include horizontal portions and bendsconnecting the horizontal portions.

Preferably at least most of the fluid circuit portion is within a finnedportion of an evaporator.

The heat pump may include a control arrangement configured to vary,between non-zero values, a speed of the fluid pump.

The fluid pump and the reversing valve arrangement may be mechanicallyconnected so that they may be handled as a single unitary body, i.e. toform a pump-and-valve unit. This aspect of the invention also providesthe pump-and-valve unit. Alternatively, the components of thepump-and-valve arrangement may be distributed with suitable fluidconnections therebetween.

Another aspect of the invention provides a heat pump including

a fluid circuit; anda sensor to sense at least one of pressure and temperature of the fluidon a high-pressure side of the fluid circuit; anda control arrangement configured to vary, between non-zero values, aspeed of the fluid pump in response to the sensor and in positiverelation to the at least one of pressure and temperature.

‘Between non-zero valves’ and similar wording are used herein todistinguish the varying the speed from the trivial case of the varyingthe speed being simple activation or deactivation.

The control arrangement may be configured to vary the speed in positiverelation to a load on the heat pump.

The heat pump preferably includes a sensor to sense at least one ofpressure and temperature of the fluid on a high-pressure side of thefluid circuit. The control arrangement may be configured to vary thespeed in response to the sensor and in positive relation to the at leastone of pressure and temperature.

The heat pump may include a refrigerant-cooling fan for driving airthrough a heat exchanger downstream of the fluid pump. The controlarrangement may be configured to vary a speed of the refrigerant-coolingfan in response to the sensor and in positive relation to the one ofpressure and temperature.

Preferably the heat pump includes

a refrigerant-heating fan for driving air through a heat exchangerupstream of the fluid pump;a temperature sensor for providing an indication of a temperature of thematerial to be cooled by the heat pump;the control arrangement being configured to vary a speed of therefrigerant-heating fan in response to the temperature sensor and inpositive relation to the temperature of the material to be cooled by theheat pump.

Another aspect of the invention provides a heat pump including a fluidpump and a control arrangement configured to operate the fluid pump atan idle speed.

Another aspect of the invention provides a method of operating a heatpump including operating a fluid pump of the heat pump at an idle speed.

Another aspect of the invention provides a vehicle, e.g. self-propellingland vehicle, having an occupant-carrying interior heated by a heatpump.

Advantageously the vehicle may be fitted with a solar panel to power thepump. The sun roof of some vehicles may be a convenient point to placethe solar panel.

Another aspect of the invention provides a transportable container, e.g.a shipping container or smaller refrigerated unit, including

an interior;a heat pump to at least one of heat and cool the interior; anda battery for powering the heat pump.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically illustrates a heat pump;

FIG. 2 is a perspective view of a portion of a compressor;

FIG. 3 is a cross-section view of the portion of FIG. 2 ;

FIG. 4 schematically illustrates a reversing valve in a first operatingmode;

FIG. 5 schematically illustrate the reversing valve in a secondoperating mode;

FIG. 6 is a side view of a valve plate;

FIG. 7 is a cross-section view of a magnetic coupling;

FIG. 8 is a side view of a petal;

FIG. 9 is a cross-section view of a pair of ports;

FIG. 10 is a front view of a connection arrangement;

FIG. 11 is a top view of the connection arrangement;

FIG. 12 is a rear view of a pump-and-valve arrangement;

FIG. 13 is a flow chart illustrating a start-up cycle;

FIG. 14 charts cabin temperature over time;

FIG. 15 charts the speed of selected components;

FIG. 16 illustrates an evaporator of the prior art; and

FIG. 17 illustrates an evaporator according to an exemplary embodimentof the present application.

DESCRIPTION OF EMBODIMENTS

The inventor's earlier compressor 5 includes a mechanical transmissionfor transmitting power into the housing 13. Shaft power is conveyed bythe input shaft 31. The sealing arrangement 39 incorporates a lip sealacting on the shaft 31 to prevent the escape of refrigerant from theinterior 41 to atmosphere. The inventor's studies have shown that:

-   a) pressure within the volume 41 can exceed 600 kPa (87 psi) when    the compressor 5 is working hard on a hot day;-   b) the seal 39 cannot reliably seal against these pressures and as    such refrigerant is sometimes lost to atmosphere;-   c) power is lost to the friction between the seal 39 and the shaft    31; and-   d) the friction and the power loss increase in positive relation to    the pressure within the volume 41.

Accordingly, a compressor having a magnetic transmission in the form ofthe magnetic coupling 49 in place of a mechanical transmission isproposed. The magnetic coupling 49 incorporates an external rotor 51 andan internal rotor 53 separated by housing portion 55. The housingportion 55 includes a radial mounting flange carrying an array of boltholes and by which the housing portion 55 is mounted and sealinglyengaged with a front of the body 15. The housing portion 55 defines aclosed cup including a cylindrical wall 55 b extending from the flange55 a, and an end face 55 c.

The external rotor 51 is shaped to embrace the cup 55 b, 55 c andincludes magnets 51 a positioned to revolve about and in close proximityto the cylindrical wall 55 b. The internal rotor 53 includes magnets 53a positioned to revolve within and in close proximity to the cylindricalwall 55 b.

The internal rotor 53 forms part of a crank member 29′ (FIGS. 10 and 11). The external rotor 51 is connected to a source of shaft power. Thissource is preferably an electric motor. The magnets 51 a, 53 a aremagnetically co-operable such that the magnets 53 a follow the magnets51 a as a result of the magnetism operating through the housing portion55. As such shaft power is magnetically transmitted into the housing 13(from the rotor 51 to 53) without friction losses or the risk of leakageassociated with a seal akin to the seal 39.

The coupling 49 includes both external magnets 51 a and internal magnets53 a. Other variants are possible. By way of example, the magnets 51 amight be replaced with steel (or other material) magneticallyco-operable with the magnets 53 a. For the avoidance of doubt,‘magnetically co-operable material’ and similar terms as used hereintake in both magnets and non-magnets.

The coupling 49 incorporates rotationally-driven external magnets 51 ato create a rotating magnetic field by which the internal rotor 53 isrotated. In another variant of the compressor, the external rotor 51 isreplaced by a stator co-operable with the rotor 53 to form an electricmotor whereby the stator electrically creates a rotating magnetic fieldby which power is magnetically transmitted into the housing 13.

Another possibility is to place the stator inside the housing 13, inwhich case a magnetic transmission in the form of a wireless powertransfer may be employed to transmit power into the housing 13.Alternatively, an electrical transmission in the form of simple wires(or other conductor(s)) may be employed. Of course, sealing about one ormore wires is simpler than sealing about the input shaft 31 and does notentail the friction losses associated with the seal 39.

The improved sealing offered by an electrical and/or magnetictransmission helps to minimise the weight of the compressor. Someexisting compressors are mounted within a sealed canister to capture anyrefrigerant leaking therefrom. The improved sealing allows for theelimination of the canister and its weight. It also contributes to thereliability of the heat pump, particularly on hot days when the pump isworking hardest. On hot days, refrigerant pressure can built up withinthe canister of canister-sealed systems such that refrigerant iseffectively lost from the fluid circuit, reducing the performance andreliability of the system.

The addition of a sealant, such as LOCTITE™, to the metal-to-metalinterfaces between the body 15, plate 25 b and head portion 25 isanother possible precaution against leakage.

Preferred forms of the compressor, including the electric drive motor,weigh less than 6 kg. To the inventor's knowledge, this is much lighterthan commonly available compressors delivering comparable output.

FIGS. 10 and 11 illustrate a preferred connection arrangement 57 bywhich the pistons 23′ are driven. The connection arrangement 57 is aform of Scotch Yoke including a single connecting member 59 having arespective one of the two pistons 23′ at each of its ends.

For the avoidance of doubt, as various terminology is used herein:

-   -   ‘member’ and similar terms refer to a single unitary body which        may be integrally formed or made up of separate,        rigidly-connected, bodies of material;    -   ‘integrally formed’ refers to a member formed of a single        continuous body of material; and    -   components may be integrated by welding but not by typical        mechanical fastening techniques.

One advantage of the connection arrangement 57 over the connectionarrangement 45 is that it enables the cylinders 21′ to be moved intocoaxial alignment to enable the sleeve-receiving bores to be machined ina single operation from one end of the block 15. This reducesmanufacturing costs. The block 15 may be formed by metal injectionmoulding. The co-axial alignment is advantageous in this context becauseit enables the sleeve-receiving bores to be cored from one end of theblock.

Whilst, in principle, the member 59 and pistons 23′ could be parts of acommon integrally formed member, preferably they are separate members.In this example, each piston 23′ is connected to the connecting member59 via a respective gudgeon pin. Whilst there is no need for the gudgeonpin to work through a range of angles associated with the movement of aconventional conrod, a very small degree of movement is desirable inthat it enables each of the pistons 23′ to self-align within itsrespective cylinder bore 21′ to account for any misalignment between thebores 21′ as a result of manufacturing tolerances and/or deformations inuse resulting from thermal and/or mechanical stresses.

Separately forming the components also enables different materials to beused. The pistons 23′ and cylinders 21′ are preferably formed ofsubstantially the same material, or at least of materials selected tohave substantially identical thermal coefficients, so as to expand atthe same rate as the components heat up in operation.

In this case, the components 19′, 23′ are formed of cast iron selectedfor its self-lubricating properties. The cylindrical surfaces of thesecomponents are ground to form accurate finishes to provide asatisfactory compromise between sealing and friction without the needfor piston rings or any similar sealing arrangements. In one variant,the cylinder is ground to a diameter in the range of 16.002 mm to 16.005mm (0.63 in to 0.63012 in) and to a surface roughness not greater than0.8. The exterior of the piston is ground to a diameter in the range of15.997 mm to 16.000 mm (0.62980 in to 0.62992 in) and within the sameroughness tolerance.

The connecting member 59 has at its centre an oval-shaped aperture 61 inwhich the pin 35′ is mounted. The pin 35′ is mounted eccentrically(relative to the axis about which the crank member 29′ rotates) todescribe a circular path. Whilst following the circular path, the pin35′ races around the periphery of the oval-shaped opening 61 to drivethe member 59 and pistons 23′ connected thereto to reciprocate.

The shape of the hole 61 and the shape and eccentricity of the pin 35′may be varied to vary the stroke and acceleration curves of the pistons.The crank members 29, 29′ and connection arrangements 45, 57 are but twoexamples of a range of possibilities. ‘Crank member’ is used herein torefer to a rotationally-driven member having at least one eccentricportion by which the piston(s) is/are driven to reciprocate. By way ofexample, the crank member could be a cam and the connection arrangementcould be a cam-following arrangement.

In each of the described arrangements, the crank member and theconnection arrangement co-operate to drive the pistons in unison so asto hold substantially constant the internal volume 41. Otherarrangements are possible. By way of example, with reference to FIG. 3 ,the crank 29 may be modified to define a pair of connecting rod journals180° apart, whereby the pistons 23 are driven in opposition to eachother so that (with the addition of a suitable inlet and outlet) thevolume 41 becomes another pumping chamber. For the avoidance of doubt,such a pumping chamber is ‘sealed to capture blow-by’ as those words andsimilar words are used herein.

The present inventor has recognised that most refrigerants havelubricating properties adequate to lubricate the pistons and cylindersand provide some resistance to blow-by. Blow-by into the interior 41provides sufficient lubrication for the crank member 29′ to operatewithout additional lubricating oils. Accordingly, preferred forms of thecompressor 5 operate without an additional volume of oil within thehousing 13 and as such losses associated with moving this oil areavoided. R134A and HR30 are the preferred refrigerants.

The inventor has also found room to significantly improve the efficiencyof the reed valves. In the inventor's earlier variants, the petals 46sealed against the planar face of the valve plate 25 b in conventionalfashion. The inventor's studies suggested that the petals 46 adhere tothe planar surface and that, with each stroke of the compressor, work isrequired to break the petals away from this adherence. The studies alsosuggest that some petals twisted along their long axes rather than fullylifting away from their ports and therefore imposed some restriction toflow.

To address this issue, the modified valve seats illustrated in FIG. 9have been developed. FIG. 9 illustrates a cross-section view through theinlet and outlet ports. Each of the ports is surrounded by a respectiveridge 63 to present the petal 46 with an edge to seal against in placeof a planar surface. Desirably, the contact area (between the petal andthe ridge 63) is not more than 20% of the area of the port.

The valve plate 25 b is formed of 3 mm thick stainless steel and theports 25 c′, 25 d′ have finished internal diameters of 6 mm. The plateis laser-cut. The holes for the ports are initially cut undersized andthen subject to a drilling operation. The drill is operated at a slowrpm and rapid rate of advance whereby consistent burrs respectivelysurrounding each end of each hole are formed. This drilling operationtakes the holes to their finished size(s). The resultant downstream burris then lapped to define a consistent sealing edge for the petal 46.

The burr is then removed from the upstream edge of the outlet port 25 c′so as not to interfere with the petal 46 for the inlet port 25 d′. Theburr may also be removed from the upstream side of the inlet port 25 d′.

Another possibility, instead of the described drilling and lappingoperations, is to fit the plate with suitable ridge-defining inserts.This may be preferable for mass production. Metal injection moulding isanother possibility for the valve plate. Optionally, the apexes of theridges may be subject to a post-moulding material-removal operation(e.g. lapping).

The inventor's testing identified the petal 46 as a potential failurepoint and it has been discovered that this can be addressed by takingadvantage of the anisotropic properties of the spring steel. Earlyfailures of the petal were associated with cracking in the vicinity ofthe root portion of the petal. Preferably the petals are cut so thattheir long axis (which is perpendicular to the axis of bending) is atleast approximately parallel to the axis along which the steel isrolled. The axis along which the steel is rolled is believed to becoincident with the orientation of the steel's grain structure.

Testing suggests that the disclosed sealing ridges also improve thereliability of the petals by at least reducing torsional loads on thepetals associated with twisting about their long axes.

The inventor's early testing has focused on two variants of thecompressor both of which have a stroke of 8 mm (0.31 in). One varianthas a bore of 16 mm (0.63 in) corresponding to a displacement of 3.2 cc(0.20 ci) for the compressor. The other variant has a bore of 17.5 mm(0.69 in) corresponding to a displacement of 3.9 cc (0.24 ci). Bothvariants are configured to operate at about 2,100 rpm.

The pump 5 is an example of a positive displacement pump. Other positivedisplacement pumps are possible. Indeed, some aspects of the inventionmay be implemented with non-positive displacement pumps such ascentrifugal pumps.

The inventor has discovered that conventional reversing valves (such asthe reversing valve 47) are not reliable when used with smallcompressors (say up to 10 cc). Practical design considerations dictate aless than perfect seal between the pistons 51 a, 51 b and the interiorof the housing 49 such that the valve does not reliably change mode whendriven by such a small compressor. By way of example, with reference toFIG. 4 , when the solenoid is switched to pressurise the chamber 51 c,the high-pressure fluid leaks past the valve 51 a without buildingsufficient pressure in the chamber 51 c to move the shuttle 51. Thisproblem came as a surprise to the inventor.

To address this non-obvious problem, the inventor proposes to replacethe refrigerant-driven valve element 51 with one or moreelectromechanically-driven valve elements, e.g. a solenoid could beadded to the valve 47 to electromechanically drive the shuttle 51. Thiswould allow the small three-way solenoid and the associated capillarytubes to be eliminated.

FIG. 12 illustrates another implementation of this aspect of theinvention. FIG. 12 is a rear perspective view of a pump-and-valve unit65 including the compressor 5 and a valve arrangement 67.

The valve arrangement 67 incorporates ports 5 _(in)′, 5 _(out), 7″ and11″. The ports 5 _(in)′, 5 _(out)′ are respectively connected to thecompressor's inlet and the outlet. Plumbing 69 in the form of coppertubing defines a T-piece connecting the port 5 _(out)′ to each of theports 7″, 11″. One arm of the T-piece carries a first first-modesolenoid S_(FM1) which, when open, defines a first first-mode flow pathakin to the flow path FP_(FM1) and mutually connecting the ports 5_(out), 7″. The other arm of the T-piece carries a first second-modesolenoid S_(SM1) which, when open, defines a first second-mode flow pathakin to the flow path FP_(SM1) and mutually connecting the ports 5_(out)′, 7″.

The unit 65 further includes further plumbing 71 defining anotherT-piece equipped with solenoid valves S_(FM2), S_(SM2) for alternatelyconnecting the port 5 _(in)′ with one or the other of the ports 7″, 11″.

This arrangement advantageously thermally separates the first-mode flowpaths from each other and the second-mode flow paths from each other, toavoid heat exchange therebetween (as may occur within the valve 47) tolead to further efficiency gains.

In operation, only a diagonally-opposed two of the four solenoid valvesare open at any one time. All four valves change state to change theoperating mode. By way of example, to switch from the first operatingmode to the second operating mode, the first-mode solenoid valvesS_(FM1), S_(FM2) are closed and the second-mode solenoid valves S_(SM1),S_(SM2) are opened.

The valve arrangement 67 incorporates four two-way solenoid valves.Another possibility entails one or more three-way valves. Any adjacenttwo of the four two-way solenoid valves could be replaced by a suitablethree-way valve.

The described arrangements of one or more electromechanically-drivenvalve elements enables smaller than conventional heat pumps to reliablyreverse cycle.

The solenoid valves are preferably 12V solenoid valves to operate fromthe same power supply as is the compressor. For the avoidance of doubt,the movable fluid-contacting portion of a conventional solenoid valve isan electromechanically-driven valve element as those words and similarwords are used herein.

The present inventor has also discovered that, in the context ofextraordinarily small heat pumps, the evaporator can be a source ofinefficiency. FIG. 17 illustrates a preferred form of evaporator 311including an inlet 313, an outlet 315, and a fluid path portion 317connecting the inlet to the outlet. The evaporator 311 is essentiallythe evaporator 211 turned on its side so that the vertical runs 219become horizontal runs 319, and downward bends 221 a become upward bends321 a. The inventor's tests suggest that dramatic improvements inefficiency can be realised through this simple reorientation and thatthis efficiency gain is achieved by eliminating the gas-traps defined bythe downward portions of the fluid path 217.

The inventor has recognised that as the refrigerant evaporates along thepath 217 it becomes relatively buoyant, and that along the downward runs219 b this buoyancy provides a resistance against which the compressormust work.

In the heat exchanger 311 the buoyancy of the vapor urges therefrigerant to flow in the same direction as it is urged to flow by thefluid pump 5. More specifically:

-   -   through the upward portions of the bends 317 the buoyancy of the        vapor urges the refrigerant to flow in the same direction as it        is urged by the pump 5; and    -   along the horizontal runs 319 the buoyancy at least does not        resist the urging of the fluid pump 5.

In the illustrated example, a single serpentine path connecting theinlet 313 to the outlet 315 is disclosed. Other options are possible. Byway of example, the relevant portion of the fluid circuit may be made upof two parallel flow path portions.

Preferably all mixed-phase portions of the low-pressure side of thefluid circuit are upward or at least horizontal. Likewise, preferablythere are no downward portions in the fluid path portion within theevaporator, although it is possible that a downward run of conduit mightbe added to a single-phase portion of the flow path within theevaporator, e.g. for more convenient connection to the expansion valveor the compressor, without a dramatic reduction in efficiency.

The inventor's studies into the reliability of heat pumps have alsorevealed that many failures occur at start-up as opposed to when theheat pump is pumping heat. Many of these failures have been found torelate to the torque necessary to start the compressor. In an inactiveheat pump, significant pressure can build in the fluid circuit,including in the pumping chamber, such that the torque required to movethe piston is more than the electric motor is capable of, e.g. thecurrent draw from the motor may exceed an enforced current limit, e.g.may blow a fuse. As such, automotive air conditioners are notorious forbeing least reliable when they are most needed, i.e. on the hottestdays.

The present inventor's adoption of two smaller pistons (having theircompression and suction strokes out of phase to each other) as opposedto a single larger piston is a first step to addressing the start-upproblems. Having a variable-speed drive unit (e.g. electric motor)dedicated to the compressor is another step in the right direction andis in stark contrast to the conventional approach of driving acompressor by selective engagement with a vehicle's combustion engine.The dedicated drive allows the compressor to be driven at a speed thatis most efficient for the particular operating conditions rather than tobe driven at a speed corresponding to the combustion engine, which maywell lead to sub-optimal operation of the compressor and the heat pump.

Providing a dedicated variable-speed drive allows for the convenientimplementation of new control strategies to improve the performance ofthe compressor and/or heat pump and to address the risk of failure atstart-up.

The present inventor has recognised that the start-up problems can belargely avoided by operating the compressor at an idle speed rather thanallowing the compressor to shut down completely (e.g. at the whim of athermostatic controller). The inventor's prototypes have been tested atan idle speed of 1,000 rpm at which their electric motors each drawabout 5 amps at about 12 volts (i.e. at about 60 watt). When thecompressor is operated at this speed, the heat pump 1 providesnegligible heating performance. The fans 7 a, 11 a may be deactivated orat least slowed or operated on a low-duty cycle.

Whilst the about 60 watt idle-speed power draw results in some wasterelative to simply deactivating the system, the inventor has found thatunder typical automotive operating conditions this waste is more thanoffset by the other efficiencies of the disclosed methods and apparatus.

The 60 watt/1000 rpm idle speed is achieved using Allied Motion'sPJ2P021Q electric motor. Of course, other electric motors (and indeedother drive arrangements more generally) are possible. Direct current12V, 36V or 48V drives are preferred to suit automotive applications.

The inventor's studies have shown that many existing 12V vehicleelectrical systems are capable of supplying the compressor with 20 ampsfor a sustained period. Preferred variants of the disclosed heat pumpshave a coefficient of performance of at least 4 whereby utilising theavailable 20 amps at 12V (240 watt) they are capable of delivering about900 watts or more of heating and/or cooling within the 20 amp currentlimit.

The start-up problems are most significant on hot days during which theheat pump may well operate almost continuously. Accordingly, to suitsome applications, it may be appropriate to enter the idle-speed modebased on an indication of the ambient temperature. By way of example:

-   -   if the ambient temperature is above a predetermined threshold,        when the heat pump is likely to be operating at least most of        the time, the heat pump may enter the idle-speed mode if and        when the pump is deactivated (e.g. deactivated by a thermostatic        controller); and    -   if the ambient temperature is below a predetermined threshold        (and restarting is unlikely to be problematic), the heat pump        may be deactivated in conventional fashion.

To implement these control strategies, the heat pump 1 may include acontroller 71, an ambient temperature sensor 73, a cabin (or othertarget) temperature sensor 75 and a pressure sensor 77. The controlarrangement 71 is configured to receive data from the sensors 73, 75, 77and to send control signals to the components 5, 7 a, 11 a. The variouscomponents are preferably connected by suitable wired links, althoughwireless connections are also possible. Various of the components may beintegrated and/or commonly housed.

FIG. 13 illustrates a preferred control logic implemented by the controlarrangement 71. FIGS. 14 and 15 illustrate the results of that logic.Again, by way of example, the invention is described with reference tocooling the interior of a truck cabin, although of course the disclosedprinciples are applicable to other contexts. At step 101, the controlprocess is initiated, e.g. upon ignition of the truck's combustionengine. At step 103, the output of the sensor 75 is checked to determinewhether the sensed temperature is above a threshold, e.g. 45° C. If not,the control arrangement 71 moves on to pressure control mode at step105.

On hotter days, the control arrangement moves on to increment a counterat step 107, and then to check whether the counter is above thethreshold corresponding to, for example, 15 minutes. Whilst the counterremains below the threshold, the controller moves on to operation in anoverspeed mode at step 111.

In the overspeed mode, the compressor is operated faster than itscomponents are intended for continuous operation, to maximise thecooling effects. For the same reason, the condenser fan 7 a is alsooperated at about 20% above its typical operating speed. The internalfan is also operated at about 10% more than its peak efficiency speed.The peak efficiency speed is the speed at which the air it moves rejectsthe most heat (as measured by power) to the refrigerant for a giventemperature of the air being moved.

Overspeeding the fan serves to stir the air within the truck cabin. Inparticular, the hottest pools of air around the ceiling of the cabin,which can be as hot as 80° C. (176° F.) are moved. When the air isrecirculated within the truck cabin, the displacement of these hot poolsof air leads to hotter air moving through the evaporator 11 and therebyto improved cooling. The illustrated cycle continues to iterate untilthe end of the preset period for the overspeed mode, whereupon (at step109) the control 71 moves on to the pressure control mode at step 105.

Other variants are possible. By way of example, between steps 107 and111 the sensor 75 may be rechecked. The control arrangement may move tothe pressure control mode if the cabin temperature drops below athreshold which may or may not be the same threshold as the overspeedmode entry threshold (at step 103).

The pressure control mode is so named because the speed of the condenseris controlled in positive relation to the pressure on the high-pressureside of the fluid circuit 3, e.g. in response to the sensor 77. Thiscontrol arrangement advantageously leads to efficient steady-stateoperation of the heat pump, in stark contrast to conventional stop-startthermostatic control and sub-optimal compressor speed.

The pressure on the high-pressure side of the fluid circuit provides anindication of the load on the heat pump. Other indicators of load may berelied upon to control the heat pump.

For the avoidance of doubt, ‘in positive relation’ means ‘to increasewith’. Over the domain of positive real numbers, y=ax, y=ax², y=a^(x)and y=log x are examples of positive relationships.

The speed of the external fan 7 a is also controlled in positiverelation to the pressure of the high-pressure refrigerant. In otherexamples of the invention, the air flow to a heat exchanger may becontrolled in other ways, e.g. in the context of a truck, instead ofaccelerating the fan 7 a, a vent may be opened to allow for more airmovement as a result of movement of the truck.

The speed of the internal fan 11 a is controlled in positive relation tothe cabin temperature, e.g. controlled in positive relation to an amountthat that temperature exceeds a set desired temperature. The desiredtemperature is 22° C. in this example. Preferably the speed of the fan11 a is also limited to the peak efficiency speed.

FIG. 14 illustrates the internal temperature of a truck that has beenactivated after it has been left stationary in the sun for some time. Atstart-up (i.e. at step 101), the sensor 75 indicates a temperature of60° C. As described, the pump 1 (or more specifically its controller 71)enters the overspeed mode for a period of 15 minutes until step 109′whereat the pump switches to the pressure control mode. During theoverspeed mode, the temperature within the cabin decays at anexponential rate. Upon switching to the pressure control mode, theefficiency of cooling increases and as such there is a shallow knee inthe graph. Thereafter the temperature in the cabin continues to decay atan exponential rate until about the 30 minute mark whereat thetemperature approximates a steady 22° C. and the heat pump iscontinuously operating to provide efficient cooling matched to the heatentering the cabin from other sources.

The described heat pump is particularly advantageous in and for thecontext of vehicles wherein its compact size, light weight andreliability are particularly advantageous.

As noted, electrically-driven variants of the heat pump allow for thecompressor to be operated at speeds independent of the crank speed ofthe vehicle. It also enables the heat pump to be moved away from theengine. The costly and often problematic drive belt for driving thecompressor can be eliminated.

The conventional placement of automotive air conditioners towards thefront of the engine bay presents other problems. Since the compressor ispositioned to be driven off the engine's crank shaft, it typicallyfollows that the condenser is positioned foremost in the engine bay infront of the engine's radiator. At this location, the condenser istypically in prime position to be damaged during minor road accidents.Vast quantities of refrigerant are lost to atmosphere in this way. Thiscauses environmental damage. The damage to the air conditioner also addsto the cost of the crash repair. The adoption of an electrically-drivencompressor enables the entire heat pump to be conveniently relocated toa safer position, e.g. towards the rear of the vehicle whereto suitablecooling air may be ducted.

The overall efficiency of the heat pump also lends itself to the ongoingoperation of the heat pump whilst the vehicle's combustion engine isdeactivated. In many parts of the world, it is not uncommon to seeunoccupied vehicles idling simply to run the air conditioner. This is ofcourse grossly inefficient and thus expensive. It also leads tounnecessary pollution.

Whilst the invention is particularly advantageous in the context ofself-propelling land vehicles, it may also be advantageously appliedelsewhere, such as in the context of yachts and other water-goingvessels. In the context of some water-going vessels, using existingtechnologies, it is not uncommon for the vessel's large diesel enginesto be idling simply to power the air conditioners. Of course, this isespecially inefficient.

The application of the described heat pump, and in particularreverse-cycle variants of the disclosed heat pump, to heat theoccupant-carrying interior of a vehicle is particularly advantageous. Atpresent, many vehicles have essentially separate heating and coolingsystems. The heating systems have a ‘water core’ through which heat istransferred from the water of the combustion engine to air to heat theinterior. Of course, these cores entail some cost, some weight and somerisk of failure. Advantageously these cores (and the associated fans,etc) can be eliminated by adopting the disclosed heat pumps. Asdescribed, the same heat exchanger that cools the cabin can be employedto heat it when the vehicle is exposed to colder weather.

Early variants of the compressor 5 were developed to provide airconditioning to the helmets of race-car drivers racing at an elite levelwhereat high performance, minimum weight and absolute reliability areessential under very challenging conditions. As such, the compressor 5has been proven to inertial loadings up to 8G. With the continueddevelopment of the concept disclosed herein, the pump's performancecontinues to surprise and impress. A test of a variant of the heat pumppowered by a N70ZZ battery and a 250 watt solar panel to cool a 5.5 m(18 ft) caravan was highly successful.

The integration of the described heat pump with battery solar systems isparticularly advantageous. In such systems, the efficiency of thedisclosed heat pump is a clear advantage. The improved start-upcharacteristics of the compressor are also important. Many such systemswhich cannot supply the electrical current necessary to start aconventional heat pump of similar scale (or can only do so when theirbatteries are in good condition and fully charged) can reliably start upthe disclosed heat pump over a wide range of battery conditions. This isparticularly advantageous in the context of water-going vessels anddwellings that are not connected to a mains power supply.

Some vehicles may be equipped with two or more of the disclosed heatpumps. By way of example, a limousine may be fitted with separate heatpumps for the driver and each of two or more passengers in the rear ofthe vehicle to enable each of the occupants to have separatelycontrolled heating and cooling.

Optionally, a vehicle may be connected to mains power whilst it isstationary, to operate the heat pump as required. By way of example, incolder climates the heat pump may be operated overnight to provide acomfortable interior for the driver in the morning.

Various examples have been described. The invention is not limited tothese examples. Rather, the invention is defined by the claims. By wayof example, the disclosed heat pump may be employed for heatingsubstances other than air. Likewise, whilst a fluid pump for pumpingfluid about the fluid circuit of a heat pump has been described, thedisclosed fluid pumps may find application elsewhere. In particular, thecompressor 5 is particularly advantageous when used as a vacuum pump toevacuate the fluid circuit of a heat pump.

For the avoidance of doubt, a typical combustion engine is an example ofa fluid pump, driven by the release of chemical energy from fuel, as‘fluid pump’ and similar terminology is used herein albeit thatpreferred forms of the disclosed fluid pumps are driven by sources ofmore organized power, such as sources of shaft or electrical power.

The term ‘comprises’ and its grammatical variants has a meaning that isdetermined by the context in which it appears. Accordingly, the termshould not be interpreted exhaustively unless the context dictates so.

1. An apparatus comprising: a fluid pump, the fluid pump including: oneor more piston-cylinder arrangements each including a respective pistonportion and a respective pumping chamber; a crank member; a housing; anda transmission; the housing together with the respective piston portionof each of the one or more piston-cylinder arrangements defining aninterior in which the crank member is housed; the interior being sealedto capture blow-by; and the transmission being arranged to transmitpower, for rotating the crank member, into the housing magnetically,electrically or both magnetically and electrically.
 2. The apparatus ofclaim 1 wherein the transmission comprises a magnetic couplingincluding: a rotatable portion outside the housing; and a portion insidethe housing magnetically co-operable with, to be rotated by, therotatable portion.
 3. The apparatus of claim 2 including an electricmotor for driving the rotatable portion.
 4. The apparatus of claim 1including an electric motor having a stator and a rotor, which arelocated inside the housing.
 5. The apparatus of claim 4 wherein thetransmission includes at least one wire for the electric motor and whichenters the housing via a sealed aperture.
 6. The apparatus of claim 1wherein the transmission includes an electric motor comprising: a statoroutside of the housing; and a rotor inside the housing.
 7. The apparatusof claim 1 including two or more of the piston-cylinder arrangements. 8.The apparatus of claim 7 including one or more connecting arrangementsconnecting the crank member to the respective piston portions, whereinthe crank member and the one or more connecting arrangements areconfigured to move the respective piston portions in unison to holdsubstantially constant a volume of the interior.
 9. The apparatus ofclaim 8 wherein the one or more connecting arrangements include a memberhaving: two ends; and a respective one of the piston portions at each ofthe ends.
 10. The apparatus of claim 1 comprising reed valves eachincluding: a respective port; a respective ridge surrounding therespective port; and a respective petal arranged to bear against therespective ridge to close the respective port; wherein each respectiveone of the pumping chambers has a respective first of the reed valvesdefining one of an inlet to the respective pumping chamber and an outletfrom the respective pumping chamber.
 11. The apparatus of claim 10wherein each respective ridge is shaped to contact a respectivelycorresponding respective petal along a respective line of contact notmore than 0.5 mm thick.
 12. The apparatus of claim 11 wherein eachrespective one of the pumping chambers has a respective second of thereed valves defining the other of the inlet to the respective pumpingchamber and the outlet from the respective pumping chamber.
 13. Theapparatus of claim 10 wherein pistons have a combined displacement ofnot more than 10 cc (0.61 ci).
 14. The apparatus of claim 1 wherein theapparatus is a heat pump and includes a fluid circuit; and the fluidpump is arranged to pump fluid about the fluid circuit.
 15. Theapparatus of claim 14 wherein the apparatus is a reverse cycle heat pumpand includes a reversing valve arrangement; and the reversing valvearrangement includes: first-mode flow paths through which fluid flowswhen the pump is in the first mode of operation; second-mode flow pathsthrough which fluid flows when the pump is in the second mode ofoperation; one or more valve elements; and one or more electromechanicaldrives; and the one or more electromechanical drives are arranged toelectromechanically drive the one or more valve elements: from one ormore respective first-mode positions at which the one or more valveelements occlude the second-mode flow paths; to one or more respectivesecond-mode positions at which the one or more valve elements occludethe first-mode flow paths; to reverse a direction of flow about thefluid circuit and thereby switch from the first operating mode to thesecond operating mode.
 16. The apparatus of claim 14 configured forevaporation of the fluid when the heat pump is in at least one operatingmode of the heat pump, and wherein: the fluid circuit includes a fluidcircuit portion; the fluid circuit is configured for at least most ofthe evaporation to occur along the fluid circuit portion; and the fluidcircuit portion is arranged for the fluid to flow upwardly, or at leasthorizontally, along substantially all of the fluid circuit portion whenthe heat pump is in the at least one operating mode of the heat pump.17. The apparatus of claim 16 wherein the fluid circuit is configuredfor at least 90% of the evaporation to occur along the fluid circuitportion.
 18. The apparatus of claim 16 wherein the fluid circuit portionincludes a serpentine conduit portion along which the fluid flows. 19.The apparatus of claim 14 including: a sensor to sense at least one ofpressure or temperature, of the fluid on a high-pressure side of thefluid circuit; and a control arrangement configured to vary a speed ofthe fluid pump in response to the sensor and in positive relation to theat least one of the pressure or temperature.
 20. The apparatus of claim19 wherein the fluid circuit comprises: a downstream heat exchangerdownstream of a fluid pump; and a refrigerant-cooling fan for drivingair through the downstream heat exchanger; and the control arrangementis configured to vary a speed of the refrigerant-cooling fan in responseto the sensor and in positive relation to the at least one of thepressure or temperature.
 21. The apparatus of claim 19 wherein: thefluid circuit comprises an upstream heat exchanger upstream of the fluidpump; and the apparatus comprises: a refrigerant-heating fan for drivingair through the upstream heat exchanger; and a temperature sensor forproviding an indication of a temperature of the material to be cooled bythe heat pump; and the control arrangement is configured to vary a speedof the refrigerant-heating fan in response to the temperature sensor andin positive relation to the temperature of the material to be cooled bythe heat pump.